1. Field of the Invention
The present invention relates to an apparatus and method for generating a high speed dubbing signal to be recorded by an external recording system.
2. Description of the Prior Art
High speed analog dubbing of video and audio signals can be achieved, for example, by reproducing video and audio signals recorded on a tape at a speed N times the normal reproduction speed so that the pitch (or frequency) of the signals become N times that of the original signals, and by recording the reproduced signals on another tape at N times the normal speed, thereby reducing the dubbing time to 1/N times the actual time of the video and audio signals. Here, N times the normal speed means that both the tape and head drum move N times their normal speeds, respectively. This dubbing method can form the same magnetization patterns on a copy tape as those formed by real time, normal speed dubbing because the video and audio signals are reproduced from the original tape at the speed N times the normal speed, and are recorded on another tape at the same speed.
To perform such high speed dubbing, a one-inch helical analog VTR for broadcast use is commonly employed, for example. The apparatus reproduces double pitched video and audio signals by doubling both the normal head drum speed and tape traveling speed.
Thus, when a conventional one-inch helical analog VTR for broadcast use is employed in high speed dubbing, the head drum speed must be increased to 7200 r.p.m., that is, a speed twice the normal reproduction speed. However, this presents a problem in that the contact between a tape and the heads in the rotating head drum becomes unstable. Generally speaking, the floating height d of a tape over a head drum is expressed by the following equation: EQU d.varies.T.sup.-1 .times.K.sup.2/3 ( 1)
where K is the number of rotations of the head drum, and T is the tension of the tape. Equation (1) shows that the floating height d of the tape over the head drum increases with the head drum rotational frequency K. Accordingly, the tape travel on the head drum becomes more unstable as the number of rotations of the head drum increases, thereby causing greater fluctuations of the head output. To solve this problem, an increase in the tape tension T may be thought to be effective. This, however, cannot be an effective means because it increases tape damage.
On the other hand, the head output loss L due to the separation S between the head and the tape during reproduction can be expressed by the following Equation (2): EQU L=54.6.times.(S/.lambda.)db (2)
where .lambda. is a recording wavelength.
Generally, the floating height d of the tape over the head drum, and hence, the separation S between the tape and the head, increases consistently with the drum rotational frequency K. Thus, as shown in Equation (2), the output loss L of the head increases in a region where the recording wavelengths .lambda. are short so that the balance is disturbed between the upper sideband and the lower sideband of an FM modulated signal of a tape reproduction signal. This presents a problem in that the video signal is distorted during the demodulation of the FM modulated signal.
In addition, since the conventional method employs an analog VTR, the S/N ratios and the distortion characteristics of reproduced video and audio signals in the dubbing process greatly depend on the characteristics of the tape and heads, and cannot meet the specifications required.